An Evaluation of the Utility of NWRT Phased Array Radar Observations as Compared to WSR-88D in the Analyses and Forecasts of a Tornadic Supercell Storm

            An attractive feature of Phased Array Radar (PAR) is the ability to provide rapidly updating (~30-s) volumetric data. By assimilating PAR data using a four-dimensional Ensemble Kalman filter (4DEnKF), one can theoretically take advantage of the high temporal resolution to better initialize numerical forecasts of supercell thunderstorms and their attendant hazards, which is part of NOAA’s Warn-on-Forecast project goals. Analysis and forecast experiments using the 21 May 2011 Ada, Oklahoma, supercell are performed in order to quantify the utility of PAR data versus operational WSR-88D observations when assimilated using 4DEnKF. The experiments use a 40-member ensemble at 2 km grid spacing. Reflectivity and radial velocity observations were assimilated in two experiments: one using data from the nearest WSR-88D and another using data from the National Weather Radar Testbed (NWRT) PAR research radar located in Norman, Oklahoma. Analyses are produced every 5 minutes for 45 minutes, and 1-hour forecasts are launched every 15 minutes during the assimilation period.

            Results from these experiments indicate that after 30 minutes of data assimilation, the PAR experiment produced analyses that better matched NSSL Multi-Radar/Multi-Sensor (MRMS) reflectivity observations than did the WSR-88D experiment. Additionally, the 1-hour forecasts from these analyses showed a better placement of the low-level mesocyclone in the PAR experiment than the WSR-88D experiment. After 45 minutes of data assimilation, fewer differences are seen between the WSR-88D and PAR experiments. This suggests that PAR is most beneficial for a shorter assimilation period.  An additional experiment using a reduced set of tilts from the PAR confirms that the increased accuracy of the PAR experiment is primarily due to the more rapidly updating volume scans.